U.S. patent application number 17/169884 was filed with the patent office on 2021-08-12 for solid oxide fuel cell cathode materials.
This patent application is currently assigned to PHILLIPS 66 COMPANY. The applicant listed for this patent is PHILLIPS 66 COMPANY. Invention is credited to Ye Lin, Ying Liu.
Application Number | 20210249665 17/169884 |
Document ID | / |
Family ID | 1000005511701 |
Filed Date | 2021-08-12 |
United States Patent
Application |
20210249665 |
Kind Code |
A1 |
Lin; Ye ; et al. |
August 12, 2021 |
SOLID OXIDE FUEL CELL CATHODE MATERIALS
Abstract
A cathode in a solid oxide fuel cell containing AgPrCoO.sub.3.
The operating temperature range of the cathode is from about
400.degree. C. to about 850.degree. C.
Inventors: |
Lin; Ye; (Bartlesville,
OK) ; Liu; Ying; (Bartlesville, OK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PHILLIPS 66 COMPANY |
Houston |
TX |
US |
|
|
Assignee: |
PHILLIPS 66 COMPANY
Houston
TX
|
Family ID: |
1000005511701 |
Appl. No.: |
17/169884 |
Filed: |
February 8, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62972907 |
Feb 11, 2020 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 2004/8689 20130101;
H01M 4/9033 20130101 |
International
Class: |
H01M 4/90 20060101
H01M004/90 |
Claims
1. A cathode in a solid oxide fuel cell comprising: AgPrCoO.sub.3;
wherein the operating temperature range of the cathode is from
about 400.degree. C. to about 850.degree. C.
2. The cathode of claim 1, wherein AgPrCoO.sub.3 is made from Ag
doping PrCoO.sub.3.
3. The cathode of claim 1, wherein AgPrCoO.sub.3 is
Ag.sub.xP.sub.1-xCoO.sub.3 wherein x ranges from about 0.05 to
about 0.15.
4. The cathode of claim 1, wherein the cathode does not contain any
Sr.
5. A composite cathode in a solid oxide fuel cell comprising:
AgPrCoO.sub.3; and Gd.sub.0.1Ce.sub.0.9O.sub.2, wherein the
operating temperature range of the cathode is from about
400.degree. C. to about 800.degree. C.
6. The composite cathode of claim 5, wherein the weight ratio of
AgPrCoO.sub.3 to Gd.sub.0.1Ce.sub.0.9O.sub.2 ranges from 30:70 to
80:20.
7. The composite cathode of claim 5, wherein the solid oxide fuel
cell utilizes a doped ceria barrier layer.
8. The composite cathode of claim 5, wherein the solid oxide fuel
cell does not utilize a gadolinium doped ceria barrier layer.
9. The composite cathode of claim 5, wherein the cathode does not
contain any Sr.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a non-provisional application which
claims the benefit of and priority to U.S. Provisional Application
Ser. No. 62/972,907 filed Feb. 11, 2020, entitled "Solid Oxide Fuel
Cell Cathode Materials," which is hereby incorporated by reference
in its entirety
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] None.
FIELD OF THE INVENTION
[0003] This invention relates to a solid oxide fuel cell cathode
material.
BACKGROUND OF THE INVENTION
[0004] A solid oxide fuel cell (SOFC) is an electromechanical
device that continuously converts chemical energy into electrical
energy by exploiting the natural affinity of oxygen and hydrogen to
react. By controlling the means by which such a reaction occurs and
directing the reaction through a device it is possible to harvest
the electrical energy given off by the reaction.
[0005] Generally, an SOFC stack repeat unit contains multiple
layers such as a support substrate, an active anode layer, an
electrolyte layer, a barrier layer, a cathode, an interconnect, an
anode current collecting layer, a cathode current collecting layer,
an anode seal, and a cathode seal.
[0006] There exists a need for new novel cathode components for
SOFC's that would enable greater electrical output and lower
material and fabrication costs.
BRIEF SUMMARY OF THE DISCLOSURE
[0007] A cathode in a solid oxide fuel cell containing
AgPrCoO.sub.3. The operating temperature range of the cathode is
from about 400.degree. C. to about 850.degree. C.
[0008] A composite cathode in a solid oxide fuel cell. The
composite cathode comprises AgPrCoO.sub.3 and
Gd.sub.0.1Ce.sub.0.9O.sub.2. The operating temperature range of the
cathode is from about 400.degree. C. to about 800.degree. C.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] A more complete understanding of the present invention and
benefits thereof may be acquired by referring to the follow
description taken in conjunction with the accompanying drawings in
which:
[0010] FIG. 1a depicts the thermogravimetric analysis (TGA) results
of the state-of-the-art conventional SOFC cathode material
Sm.sub.0.5Sr.sub.0.5. FIG. 1a depicts
CoO.sub.3--Gd.sub.0.1Ce.sub.0.9O.sub.2 and Ag.sub.0.1. FIG. 1b
shows Pr.sub.0.9CoO.sub.3--Gd.sub.0.1Ce.sub.0.9O.sub.2.
[0011] FIG. 2a depicts the current voltage and current power
density curves of a fuel cell with
Ag.sub.0.1Pr.sub.0.9CoO.sub.3-GDC cathode tested in hydrogen at
650.degree. C. FIG. 2b is an enlarged section of FIG. 2a near 0.8
V.
[0012] FIG. 3 depicts fuel cell performance at 0.8V and 650.degree.
C. for Ag.sub.0.1Pr.sub.0.9CoO.sub.3-GDC cathode directly applied
on YSZ electrolyte and SSC-GDC cathode with a GDC barrier layer.
Cathode feed air contained 1.6% CO.sub.2.
DETAILED DESCRIPTION
[0013] Turning now to the detailed description of the preferred
arrangement or arrangements of the present invention, it should be
understood that the inventive features and concepts may be
manifested in other arrangements and that the scope of the
invention is not limited to the embodiments described or
illustrated. The scope of the invention is intended only to be
limited by the scope of the claims that follow.
[0014] As briefly introduced above, the present embodiment provides
a cathode material AgPrCoO.sub.3. The operating temperature range
of the cathode is from about 400.degree. C. to about 850.degree. C.
It is theorized that this new material when mixed with gadolinium
doped ceria (GDC) exhibits superior mixed ionic and electronic
conductivities, partially by overcoming stability issues of other
cathode materials. It is also theorized that AgPrCoO.sub.3 (APC)
show excellent long-term stability in CO.sub.2 containing
environments. In one embodiment, use of AgPrCoO.sub.3 as a cathode
material eliminates the use of barrier layers such as gadolinium
doped ceria which has the ability to significantly reduce the
material and fabrication costs of SOFCs.
[0015] In one embodiment, AgPrCoO.sub.3 is made from Ag doping
PrCoO.sub.3. This produces Ag doping levels of
Ag.sub.xPr.sub.1-xxCoO.sub.3, x=0.05-0.15. In one non-limiting
embodiment, the doping of PrCoO.sub.3 can be done by first
dissolving metal nitrate hydrates with stoichiometric ratio in
deionized water. Citric acid (CA) was added as a chelating agent
with a CA-to-nitrate-ion molar ratio of around 1:2. Appropriate
amount of ammonia water was then added to adjust the PH to
.about.6. The resulting clear solution was heated at 90.degree. C.
for a prolonged period until a clear gel was formed. The gel was
placed in an oven overnight at 150.degree. C. to form a foam. The
foam was then grinded and calcined at 800.degree. C. for around 5
hours.
[0016] For cathode ink preparation, Ag doped PrCoO.sub.3 were mixed
with GDC powder in a weight ratio of 60:40. The composite cathode
powder was further mixed with ink vehicle (Fuel cell materials) in
a weight ratio of 60:40. The mixture was milled in a high energy
ball mill at 350 rpm for 1 hour to form the cathode ink. The
cathode ink was applied onto fuel cells with a cathode area of
12.25 cm.sup.2.
[0017] Sample Preparation:
[0018] Two types of baseline cells with yttria-stabilized zirconia
(YSZ) electrolyte were produced: [0019] Type-1: NiO+YSZ anode/YSZ
electrolyte/GDC barrier layer/APC-GDC cathode [0020] Type-2:
NiO+YSZ anode/YSZ electrolyte/APC-GDC cathode
[0021] Type-1 cells had a GDC hairier layer and Type-2 cells didn't
contain a GDC barrier layer between cathode and electrolyte
layers.
[0022] The cathode was sintered at 900.degree. C. or 950.degree. C.
for 2 hours, at a 2.degree. C./min ramp rate. All fuel cells were
held at 800.degree. C. overnight in hydrogen before electrochemical
testing. The fuel cell performance was evaluated between 500 to
750.degree. C., and the impedance curves were taken at 650.degree.
C. under open circuit condition.
[0023] Type-1 Cells Evaluation
[0024] Table 1 below shows a summary of fuel cell performance with
different cathode materials at 0.8V and 650.degree. C. or
700.degree. C. Based on Type-1 fuel cells, the
Ag.sub.0.1Pr.sub.0.9CoO.sub.3-GDC cathode showed the highest
performance, which was higher than that of conventional
Sr.sub.0.5Sm.sub.0.5CoO.sub.3 (SSC)-GDC and
La.sub.0.6Sr.sub.0.4Co.sub.0.2Fe.sub.0.8O.sub.3 (LSCF)-GDC
cathodes.
TABLE-US-00001 TABLE 1 650.degree. C. 700.degree. C. and 0.8 V and
0.8 V Material Composition (mW/cm.sup.2) (mW/cm.sup.2) SSC-GDC 380
540 LSCF-GDC 377 537 SrCo.sub.0.8Ta.sub.0.1Nb.sub.0.1O.sub.3 (SCTN)
268 398 PrBa.sub.0.5Sr.sub.0.5Co.sub.1.5Fe.sub.0.5O.sub.5+.delta.
(PBSCF) 372 509 PrCoO.sub.3-GDC 308 469
Ag.sub.0.05Pr.sub.0.95CoO.sub.3-GDC 355 355
Ag.sub.0.1Pr.sub.0.9CoO.sub.3-GDC 437 636
Ag.sub.0.15Pr.sub.0.85CoO.sub.3-GDC 405 600
[0025] The performance stability of
Ag.sub.0.1Pr.sub.0.9CoO.sub.3-GDC cathode in CO.sub.2 environment
was evaluated using thermogravimetric analysis (TGA).
[0026] The TGA program was as follows:
(1) 25 to 600.degree. C., 50.degree. C./min (CO.sub.2)
(2) 600 to 650.degree. C., 10.degree. C./min (CO.sub.2)
(3) 650.degree. C., 60 min (CO.sub.2)
(4) 650.degree. C., 120 min (Air)
(5) 650.degree. C., 120 min (Argon)
(6) 650.degree. C., 30 min (Air)
[0027] FIG. 1a depicts the TGA results of (a) SSC-GDC cathode
materials. FIG. 1b depicts the TGA results of
Ag.sub.0.1Pr.sub.0.9CoO.sub.3-GDC cathode materials. As shown in
FIG. 1a and FIG. 1b, at 650.degree. C., the SSC-GDC readily
absorbed CO.sub.2, and started gaining weight due to SrCO.sub.3
formation, while the Ag.sub.0.1Pr.sub.0.9CoO.sub.3-GDC showed no
weight change. After switching to pure air, the SSC-GDC gradually
lost weight due to the decomposition of SrCO.sub.3 while
Ag.sub.0.1Pr.sub.0.9CoO.sub.3-GDC experienced no weight change in
the same period of time. After holding in air for 2 hours, a quick
switch from air to Ar was carried out. Due to the formation of
SrCO.sub.3, the SSC-GDC cathode experienced a slow weight loss
comparing to a sharp change for Ag.sub.0.1Pr.sub.0.9CoO.sub.3-GDC.
This indicated the Ag.sub.0.1Pr.sub.0.9CoO.sub.3-GDC has maintained
high oxygen reduction reaction activity/performance even after a
100% CO.sub.2 treatment. The SSC-GDC cathode, however,
significantly reduced the performance.
[0028] The migration of Sr to the surface of the cathode was found
to be an intrinsic property of the Sr containing cathode materials.
The Sr readily reacted with YSZ electrolyte and formed a
SrZrO.sub.3 insulator. To avoid the adversary reaction, a common
practice is to apply a ceria-based barrier layer at the
cathode-electrolyte interface. However, a CeZrO.sub.x solid
solution layer with much lower conductivity might form after high
temperature treatment. The CeZrO.sub.x solid solution layer could
grow in thickness under SOFC operation condition. Besides, it is
extremely hard to make a fully dense GDC layer on top of the YSZ
electrolyte. With a porous GDC barrier layer, SrZrO.sub.3 layer was
still found on the YSZ side of the GDC barrier layer and its
thickness increased over time under electrical load.
[0029] Type-2 Cells Evaluation
[0030] Table 2 below summarizes the fuel cell performance with
different cathode materials directly applied on YSZ electrolyte
(Type-2 cell). The SSC+GDC cathode was directly sintered onto the
YSZ at 950.degree. C., while both the
Ag.sub.0.05Pr.sub.0.95CoO.sub.3-GDC and
Ag.sub.0.1Pr.sub.0.9CoO.sub.3-GDC were sintered onto YSZ at
900.degree. C.
TABLE-US-00002 TABLE 2 650.degree. C. 700.degree. C. and 0.8 V and
0.8 V Material Composition (mW/cm.sup.2) (mW/cm.sup.2) SSC-GDC 22
56 Ag.sub.0.05Pr.sub.0.95CoO.sub.3-GDC 395 532
Ag.sub.0.1Pr.sub.0.9CoO.sub.3-GDC 380 554
[0031] The SSC-GDC cathode showed only 22 mW/cm.sup.2 power density
at 0.8V and 650.degree. C. due to the formation of SrZrO.sub.3
layer, while both the Ag.sub.0.05Pr.sub.0.95CoO.sub.3-GDC and
Ag.sub.0.1Pr.sub.0.9CoO.sub.3-GDC demonstrated a high performance
of over 380 mW/cm.sup.2.
[0032] The stability of the Ag.sub.0.1Pr.sub.0.9CoO.sub.3-GDC
cathode directly applied on YSZ electrolyte was evaluated in a
645.5 hours fuel cell test. The I-V curve at 650.degree. C. and
different fuel cell operation times of 195 hours, 261 hours and 605
hours are shown in FIG. 2a. FIG. 2b shows an enlarged section of
I-V curve at 650.degree. C. and different fuel cell operation times
of 195 hours, 261 hours. The 605h I-V curve was recorded after a
144 h test in 1.6% CO.sub.2 containing air and a 130 h accelerated
test with a high current density of 1368 mA/cm.sup.2. A stable
performance of 380 mW/cm.sup.2 at 650.degree. C. and 0.8V was
maintained after the long-term test as shown in FIG. 2a and FIG.
2b.
[0033] During the long-term test, the cathode feed gas was switched
from pure air to air containing 1.6% CO.sub.2. FIG. 3 shows that
the Ag.sub.0.1Pr.sub.0.9CoO.sub.3-GDC cathode reached a steady
stage during the 70 hours test in 1.6% CO.sub.2 mixed air, while
the SSC-GDC cathode showed a high degradation rate of 34.6%/kh
under the same test condition.
[0034] In closing, it should be noted that the discussion of any
reference is not an admission that it is prior art to the present
invention, especially any reference that may have a publication
date after the priority date of this application. At the same time,
each and every claim below is hereby incorporated into this
detailed description or specification as an additional embodiment
of the present invention.
[0035] Although the systems and processes described herein have
been described in detail, it should be understood that various
changes, substitutions, and alterations can be made without
departing from the spirit and scope of the invention as defined by
the following claims. Those skilled in the art may be able to study
the preferred embodiments and identify other ways to practice the
invention that are not exactly as described herein. It is the
intent of the inventors that variations and equivalents of the
invention are within the scope of the claims while the description,
abstract and drawings are not to be used to limit the scope of the
invention. The invention is specifically intended to be as broad as
the claims below and their equivalents.
* * * * *